Correct Answer: 6 days
Explanation:
Ratio of rates of working of A and B =2:1. So, ratio of times taken =1:2
Therefore, A's 1 day's work=1/9
B's 1 day's work=1/18
(A+B)'s 1 day's work= 1/9 + 1/18 = 1/6
so, A and B together can finish the work in 6 days